Cardiac hypertrophy is the major cardiac adaptation to increased mechanical work but the specific mechanical determinants and the initiating biochemical processes of hypertrophy are poorly understood. The activity of ornithine decarboxylase (EC. 4.1.1.17), the enzyme which initiates polyamine synthesis and may regulate myocardial protein synthesis, is significantly increased prior to the development and the activity of ornithine decarboxylase (ODC). The experimental model will be the isolated rabbit right ventricular papillary muscle because the mechanical variables of contractility can be accurately controlled. It is proposed to study the response of myocardial ODC to maximal developed tension and subsequently passive or resting stress, hypoxia, catecholamines and cyclic AMP modulation. It is proposed to determine the effect of developmental age on the ODC response to tension development. The proposed study will lead to a better understanding of the mechanism for the increased myocardial protein synthesis that occurs with disorders that increase myocardial tension.